Abstract. In this paper we describe a 50 years (1965–2015) ecological database containing data collected in the Northern Adriatic Sea, one of the 25 research parent sites belonging to the Italian Long Term Ecological Research Network (LTER-Italy, http://www.lteritalia.it). LTER-Italy is a formal member of the international (https://www.ilter.network) and European (http://www.lter-europe.net/) LTER networks. The NAS is undergoing a process, led by different research institutions and projects, for the establishment of a marine ecological observatory, building on the existing facilities, infrastructures, and long-term ecological data. Along this process, the implementation of the Open Access and Open Science principles has started, by creating an open research lifecycle that involves sharing ideas and results (scientific papers), data (raw and processed), metadata, methods, and software. The present data paper is framed within this wider context. The database is composed of observations on abiotic parameters, phyto- and zooplankton abundances, collected during 299 cruises in different sampling stations, in particular in the Gulf of Venice: we describe here the sampling and analytical activities, the parameters, and the structure of the database. The database is available at https://doi.org/10.5281/zenodo.3266246 (Acri et al., 2019), it was also uploaded in the DEIMS-SDR repository (Dynamic Ecological Information Management System – Site and Dataset Registry, https://deims.org/), which is the official sites and data registry for LTER International network.